Passive Optical Networks (PON) are networks of optical fiber lines in which optical light signals are transmitted and distributed without interposition of active amplifying components.
FIG. 1 is a diagrammatic representation of a conventional passive optical network 1. The passive optical network 1 shown is a so-called metro-access network by which data from e.g. a public optical fiber network 5 are distributed to a plurality of user units 4 also called ONU (Optical Network Unit) or ONT (Optical Network Termination). The optical network comprises a so-called OLT 2 (Optical Line Terminal) as access point, which is the transmission interface between the passive optical network 1 and the overlying public optical backbone fiber network 5. Moreover, the passive optical network 1 comprises a splitting unit 3 which connects a central cable 6 coming from the OLT 2 to a plurality of arms 7, each arm 7 ending at an ONU 4.
Conventional PONs are bidirectional networks, in particular they distribute downstream traffic from the optical line terminal (OLT) to optical network units (ONUs) in a broadcast manner while the ONUs send upstream data packets.
In fiber-optic communications, wavelength-division multiplexing (WDM) is a technology which multiplexes multiple optical carrier signals on a single optical fiber by using different wavelengths (colors) of laser light to carry different signals. This allows for a multiplication in capacity, in addition to enabling bidirectional communications over one strand of fiber.
WDM systems are divided into different wavelength patterns, conventional or coarse and dense WDM. WDM systems provide, e.g., up to 16 channels in the 3rd transmission window (C-band) of silica fibers of around 1550 nm. Dense WDM uses the same transmission window but with denser channel spacing. Channel plans vary, but a typical system may use 40 channels at 100 GHz spacing or 80 channels with 50 GHz spacing. Some technologies are capable of 25 GHz spacing. Amplification options enable the extension of the usable wavelengths to the L-band, more or less doubling these numbers.
Optical access networks, e.g., coherent Ultra-Dense Wavelength Division Multiplex (UDWDM) networks, are deemed to be a promising approach for future data access. Data transmission of spectrally densely spaced wavelengths is utilized by applications as Next Generation Optical Access (NGOA) systems allowing high data transmission rates of, e.g., 10 Gbit/s and more. The total amount of data handled by one system in on fiber is in the range of one terabit.
Due to the dramatically increase of data traffic in mobile applications, new concepts and architectures, like for example adding smaller cells (Micro cells) or Cloud Ran (CRAN) are under discussion in 3GPP or NGMN.
Whatever new architecture is chosen also the infrastructure—i.e. the Mobile Backhaul (MBH)—providing the necessary capacity to the Mobile Base-Stations must be adapted.
In conventional Mobile Backhaul (MBH) solutions there are Microwave Radio links, copper based connections (e.g.: E1 connections) or DSL links and optical based point to point links as well as PONs used.
For higher bandwidth in 3GPP Long Term Evolution (LTE, 150 Mbps/eNodeB) up to 3 GBps for LTE-A (LTE Advanced) mainly fiber based solutions and Microwave Radio (MWR) solutions using high frequencies (>60 GHz) with sufficient bandwidth are the most promising choices. Fiber based solution fits best providing more than sufficient capacity also for the future, whereas the digging of the fiber needs some add on for capital expenditures (Capex). This is even more valid in very dense urban areas and especially in the last mile.
MWR based solution (>60 GHz) can provide capacity in the Gbps range, however in this case distance (˜1 . . . 2 km, last mile) and “line of sight” requirement needs to be taken into account.
For the complete Mobile Backhaul (MBH) solution, therefore, a mix of fiber and MWR based infrastructure can be assumed as a very promising solution. Through the fiber infrastructure sufficient capacity for many base stations can be transported to the areas where the capacity is needed. In particular, employing MWR based solutions an easy and flexible connection for the last hundred of meters to one Base-station can be realized.
Especially for areas where a good fiber infrastructure is already available or in planning (e.g. fiber to the home FTTH coverage) a converged scenario, i.e. parallel use of the fiber based access for providing transport capacity to residential subscribers as well as for base-stations, seems to be very promising.
FIG. 2 is a diagrammatic representation of a conventional UDWDM optical transport (1st Transport Network) system connected to a Microwave Radio (MWR) transport system (2nd Transport Network). At the termination of the fiber (e.g. ONU/ONT 21) via an Ethernet based interface 22 the MWR link 23 is connected. At the termination of the MWR radio link the Base-Station eNB is connected.
In this conventional scenario both the optical transport system and the Microwave Radio (MWR) transport system need their own system specific network management with different systems characteristics. For the end-to-end supervision both system status info must be combined. This can be very complex and therefore not cost effective.
Based upon the above discussions, it is concluded that there is a need in the art, for an improved system and apparatus which allows combining an optical transport system with a Microwave Radio (MWR) transport system employing one common management system.
Furthermore, there is a need for a more flexible capacity distribution. That means e.g. that the capacity transported in one wavelength to the ONT/ONU may be shared by several subscribers.
In order to achieve such more flexible capacity distribution, it may be possible to distribute the capacity of one wavelength to several ONT via a fiber infrastructure by adapted Time Division Multiplex (TDM) mechanisms.
However, since fiber infrastructure is in some cases not available or needs big investment, there is a great demand for improvement.